ZAP-70 Protein Retains Its Prognostic Significance within Interphase Cytogenetic Groups in B-Cell Chronic Lymphocytic Leukemia (B-CLL).

Heterogeneous clinical behavior of B-CLL makes difficult for physicians to identify which pts experience a slowly progressive clinical course and which ones may benefit from an early and/or more aggressive treatment. The development of interphase FISH techniques allowed to detect selected chromosome abnormalities in non-dividing cells. In 325 CLL pts, multivariate analysis identified 17p- and 11q- abnormalities as variables associated with shorter overall survival (OS) (Dohner, 2000). Moreover, the lack of IgV_H gene mutation has been shown to predict a rapid disease progression (DP) and an inferior OS (Damle, Hamblin, 1999). B-CLL cells that use non-mutated IgV_H genes express ZAP-70 protein, associated with an enhanced B cell receptor signaling and with an early DP risk. The aims of our study were: 1) to determine progression-free survival (PFS) and OS upon cytogenetic groups and ZAP-70 expression; 2) whether ZAP-70 could predict varied outcome within interphase cytogenetic groups; and 3) whether ZAP-70 and interphase cytogenetic groups were independent prognostic factors. We investigated 216 pts, median age 64 years, 69 pts belonging to low Rai stage, 140 to intermediate stage and 7 to high stage. To date, we have completed analysis of interphase cytogenetics in 137 pts, and ZAP-70 was quantified in 216 pts by a multicolor flow cytometric method using a cut-off value of 20%. With regard to cytogenetic groups, 73 (53.3%) pts had a normal karyotype and 35 (25.5%) pts had 13q-. Twenty-nine (21.2%) pts with trisomy 12, 17p- and 11q- were pooled together and defined as “poor-risk” cytogenetic subset. ZAP-70+ pts were 81/216 (37.5%) and there was a significant correlation between high or low ZAP-70 expression and Ig V gene mutational status (P<0.00001) in 125 examined CLL pts. Furthermore, we found significant associations either between higher ZAP-70 and trisomy 12, 17p-, 11q- or lower ZAP-70 and normal karyotype (P=0.0002). With regard to clinical outcome, a shorter PFS was observed in ZAP-70+ pts (13% vs 57% at 12 years; P<0.00001) and in “poor risk” cytogenetic pts vs normal karyotype pts (9% vs 49% at 12 years; P=0.008). The 13q- pts showed an intermediate outcome (23% at 12 years). ZAP-70+ pts showed also a shorter OS (24% vs 92% at 14 years; P=0.0002). To further explore the impact of ZAP-70 among cytogenetic groups, we investigated its expression within the normal karyotype and “poor risk” CLL subsets. As a matter of fact, ZAP-70 positivity was associated both with a shorter DFS and OS in normal karyotype (16% vs 62% at 10 years, P=0.002 and 69% vs 91% at 10 years, P=0.02, respectively) and in “poor risk” pts pooled together with 13q- pts (0% vs 35% at 13 years, P=0.0017 and 24% vs 100% at 14 years, P=0.03, respectively). In multivariate analysis of PFS, only ZAP-70 (hazard ratio=6.1, P=0.01) and soluble CD23 (hazard ratio=3.9, P=0.04) resulted to be independent prognostic factors. In conclusion, ZAP-70 expression predicts significantly both DFS and OS, and varies by interphase cytogenetic group. Within normal karyotype and poor risk cytogenetic subsets, where progression is heterogeneous, ZAP-70 positivity is able to distinguish pts who have early PFS or short OS. Therefore, ZAP-70 adds prognostic information to cytogenetic data and will assist in planning therapeutic decisions for CLL pts.